In view of recent popularity of digital technology for digital video and communication satellite broadcasting, a system connecting digital devices using such a digital technology on a same network, and controlling the digital devices has been building up.
As one of a digital interface, Digital Visual Interface (DVI) is available. This interface includes a high speed signal transmission line which enables transmission of a digital video signal without compressing the signal, an Extended Display Identification Data (EDID) memory which holds information such as signal format being shown in the device at receiving side to provide to an upstream (signal source side), and a Display Data Channel (DDC) for reading out the information (for example referring to “Digital Visual Interface DVI, revision 1.0”, 2.2 Plug and Play specification, [online], Apr. 2, 1999, Digital Display Working Group, [searched on Aug. 29, 2002], www.ddwg.org/downloads.html). Furthermore the DVI includes a Hot Plug Detect (HPD) line for giving a notice of the state that the information recorded in the EDID memory being readable, and the change of the content. The HPD line enables outputting of the information indicating the change of the content, only in the case where power is supplied from the device in upstream to a device with an HPD line.
A case is considered that a control line for controlling the connected device for the interface (DVI) is added. As an example, a case is considered that a control line used for a SCART connector (CENELEC, EN 50049-1:1997/A1:1998) used in Europe is added.